jeespers85 wrote:<image>

a picture says more than a thousand words.
This what my puck looks like on my Elektra A3 after extraction. Medium to heavy channeling and inconsistent shots.

I don't know the A3; purely hypothetical:

Does the A3 use a flow restrictor? If so, does your machine have it in place? If not, high/fast water flow at the beginning of the shot could explain this? (once the basket is filled and pressurized, the flow restrictor doesn't have an impact anymore)

The A3 does have a jet IIRC it's 0.9 or 0.8 mm (compared to 0.6 mm on a newer La Marzocco machine for example); it's in the bottom of the HX chamber in the grouphead, easily accessible when you pull the group cap/bolt off (the huge chromed bolt on top of the group head assembly). You can buy a typical carburetor jet if you want a narrower jet, as detailed here. I wouldn't go too crazy with a tiny jet on the Elektra: the tighter you go, the longer it takes to do a cooling flush. It gets aggravating (I know firsthand).

Looking at your videos I would say that the flow rate is rather high.
Try to measure it! The ideal empty shot flow rate is somewhere between 2-3 oz (60-90ml) / 10sec.
Any flow rate higher than this potentially leads to channeling problems.

Try to change the group jet to a 0.6mm one!

No, don't change to the 0.6. Your cooling flush will be unbelievably long. 0.7 might be OK.

The A3 is very sensitive to dose. Assuming all other variables are acceptable (good coffee, no grinder issue, proper distribution, no wonky tamp, etc...) grind finer, lower your dose and tamp lighter. You are not going to get 16 grams of coffee in a double basket on any Elektra. If you are using the stock basket (or any basket for that matter) your dose needs to be below the rim of the basket before you tamp. If you fill/level you have too much coffee in it. For 16-18 gram doses I use a triple basket.

Thx for all inputs! I have now bought a new nozzle to a carburetor, a plus 0.6-ish mm jet. My flow is now 90 ml and channeling is now but a distant memory. But the water dance take forever and long extractions is almost impossible without overheating the water.
I imagine that is the tradeoff.

Regarding low dose, have anyone tried using an other, lower (e61) diffuser to be able to amp up the dose?

A bottomless basket and a Marzocco triple basket will get you a 19g dose. As to the flush, turn down your pressurestat. I run my machine at around 0.9 bar top of cycle and it still steams like a locomotive.

0.9 bar did the trick. Now the dance is a bit shorter. What is your experience with down-dosing and ultra-fine grinding, forced by the headspace of the Elektra, concerning the quality in the cup.

down dosing is a relative term. With the lower dispersion block (common to all Elektra machines) putting 18 grams in a 21 gram basket is not down dosed but properly dosed to allow for the shower screen clearance. The only time I have any issues is when I dose to high in the basket and do not allow adequate headspace.